Quench detector

Abstract

A quench detector for monitoring a tapped superconducting coil for changes in its conductivity and also for monitoring the integrity of the measuring leads connected to the coil. The quench detector comprises a bridge circuit including first and second resistance means having a junction therebetween connected to a first measuring point, the other ends of the first and second resistance means being connected to corresponding opposite ends of the superconducting coil. The first and second coil elements on either side of the tap of the superconducting coil and the first and second resistance means form the first branch of the bridge circuit. The second branch of the bridge circuit consists of third and fourth resistance means, each having one end connected to a second measuring point and its other end connected to the tap on the superconducting coil. The resistance of the second branch corresponds to the real or resistive, component of the impedance of the firsh branch of the bridge circuit. An operational amplifier is provided which has its first and second inputs coupled to the first and second measuring points respectively and its output coupled to the first measuring point through a fifth resistance means constituting the third branch of the bridge circuit. A sixth resistance means constituting the fourth branch of the bridge circuit is coupled between a source of test voltage and the second measuring point.

What is claimed is: 
     
       1. A quench detector for monitoring a superconducting coil for changes in its conductivity and for monitoring the leads connected to said coil, said superconducting coil being divided into first and second coil elements by a tap located between said coil elements, comprising first and second resistance means, each having means coupling one end to a first measuring point, the other ends of each of said first and second resistance means being connected to corresponding opposite ends of said superconducting coil, the first and second coil elements of said superconducting coil and said first and second resistance means forming the first branch of a bridge circuit;   third and fourth resistance means, each having means coupling one end to a second measuring point, the other ends of each of said third and fourth resistance means being connected to the tap on said superconducting coil, said third and fourth resistance means forming the second branch of said bridge circuit having a resistance corresponding to the resistive component of the impedance of said first branch;   an operational amplifier having first and second inputs coupled to said first and second measuring points, respectively;   fifth resistance means coupled between the output of said operational amplifier and said first measuring point to form the third branch of said bridge circuit; and   sixth resistance means coupled between a source of test voltage and said second measuring point to form the fourth branch of said bridge circuit.   
     
     
       2. A quench detector as defined by claim 1 wherein said second and fourth resistance means are variable and mechanically coupled to permit simultaneous setting thereof. 
     
     
       3. A quench detector as defined by claim 1 or 2 wherein said fifth resistance means comprises a fixed resistor and a variable resistor connected in series and said sixth resistance means comprises a pair of series-connected variable resistors, the variable resistor of said fifth resistance means and one of the variable resistors of said sixth resistance means being mechanically coupled to permit simultaneous setting thereof. 
     
     
       4. A quench detector as defined by claim 1 wherein the means coupling said first and second resistance means to said first measuring point comprises a first potentiometer having its ends connected to said first and second resistance means and a movable brush connected to said first measuring point, and the means coupling said third and fourth resistance means to said second measuring point comprises a second potentiometer having its ends connected to said third and fourth resistance means and a movable brush connected to said second measuring point, the movable brushes on said first and second potentiometers being mechanically coupled to permit simultaneous setting thereof. 
     
     
       5. A quench detector as defined by claim 4 which further comprises a varistor connected in parallel with said first potentiometer, said varistor protecting said first potentiometer against the generation of excessive voltages thereacross. 
     
     
       6. A quench detector for monitoring a superconducting coil for changes in its conductivity and for monitoring the leads connected to said coil, comprising first and second resistance means, each having means coupling one end to a first measuring point, the other ends of each of said first and second resistance means being connected to corresponding opposite ends of said superconducting coil,   inductive means connected between one end of said superconducting coil and said second resistance means, the junction between said inductive means and said superconducting coil being coupled to a second measuring point;   an operational amplifier having first and second inputs coupled to said first and second measuring points respectively;   fifth resistance means coupled between the output of said operational amplifier and said first measuring point; and   sixth resistance means coupled between a source of test voltage and said second measuring point.   
     
     
       7. A quench detector as defined by claim 6 wherein said inductive means comprises a normally conducting coil magnetically coupled to said superconducting coil. 
     
     
       8. A quench detector as defined by claim 6 wherein said inductive means comprises an air-core transformer having primary and secondary windings.